论文标题
$ b_q \ toγz'$的风味变化的签名
Signatures of a Flavor Changing $Z'$ Boson in $B_q \to γZ'$
论文作者
论文摘要
罕见的$ b $梅森腐烂提供了一个机会，可以探究隐藏的$ z'$ boson。在这项工作中，我们探索了一个新的频道$ b_q \toγz'$（$ q = d，s $），然后在隐形（中微子或暗物质）或带电的Lepton Pair $ \ ell^+ el^+ el^+ ell^el^ - $（$ \ ell^ - $（$ \ ell = e，e，μ）$中。该研究基于一个简化的有效模型，在该模型中，下夸克部门具有$ z'$的微小变化的中性电流耦合。我们首次以$ 1/m_b $和$ 1/e_γ$的领先功率计算$ {\ rm br}（b_q \toγz'）$。面对$ b $梅森的半衰减的强大限制，我们发现$ b_d \ to {\ rm convisible} +γ$的分支比率可能大于其标准模型预测，为新物理学留下了一个较大的房间，尤其是光线暗物质。此外，当违反$ z'$耦合到夸克的相应风味是轴向矢量类型时，$ b_d \与e^+ e^ - γ$的分支比率也很可观。另一方面，预测的分支比为$ b_d \toμ^+μ^ - γ$和$ b_s \ to \ ell^+ \ ell^ - γ$受到实验测量的严格限制。
Rare $B$ meson decays offer an opportunity to probe a light hidden $Z'$ boson. In this work we explore a new channel $B_q \to γZ'$ ($q = d, s$) followed by a cascade decay of $Z'$ into an invisible (neutrino or dark matter) or charged lepton pair $\ell^+ \ell^-$ ($\ell=e ,μ)$. The study is based on a simplified effective model where the down quark sector has tiny flavor-changing neutral current couplings with $Z'$. For the first time, we calculate ${\rm BR}(B_q \to γZ')$ at the leading power of $1/m_b$ and $1/E_γ$. Confronting with the strong constraints from semi-invisible decays of $B$ meson, we find that the branching ratio for $B_d \to {\rm invisible} + γ$ can be larger than its Standard Model prediction, leaving a large room for new physics, in particular for light dark matter. Additionally, the branching ratio for $B_d \to e^+ e^- γ$ can also be sizable when the corresponding flavor violating $Z'$ coupling to quarks is of the axial-vector type. On the other hand, the predicted branching ratios of $B_d \to μ^+ μ^- γ$ and $B_s \to \ell^+ \ell^- γ$ are severely constrained by the experimental measurements.
